Thin-film device and method of manufacturing same

ABSTRACT

A thin-film device comprises: a substrate; a flattening film made of an insulating material and disposed on the substrate; and a capacitor provided on the flattening film. The capacitor incorporates: a lower conductor layer disposed on the flattening film; a dielectric film disposed on the lower conductor layer; and an upper conductor layer disposed on the dielectric film. The thickness of the dielectric film falls within a range of 0.02 to 1 μm inclusive and is smaller than the thickness of the lower conductor layer. The surface roughness in maximum height of the top surface of the flattening film is smaller than that of the top surface of the substrate and equal to or smaller than the thickness of the dielectric film. The surface roughness in maximum height of the top surface of the lower conductor layer is equal to or smaller than the thickness of the dielectric film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin-film device comprising a lowerconductor layer, a dielectric film and an upper conductor layer that arestacked, and to a method of manufacturing such a thin-film device.

2. Description of the Related Art

With increasing demands for reductions in dimensions and thickness ofhigh frequency electronic apparatuses such as cellular phones,reductions in dimensions and profile of electronic components mounted onthe high frequency electronic apparatuses have been sought. Some of theelectronic components comprise capacitors. Each capacitor typicallyincorporates a dielectric layer and a pair of conductor layers disposedto sandwich the dielectric layer.

To achieve reductions in dimensions and profile of an electroniccomponent comprising a capacitor, important factors are a reduction inarea of a region in which the pair of conductor layers are opposed toeach other with the dielectric layer disposed in between and a reductionin the number of layers making up the capacitor. Basically, in priorart, a material having a high permittivity is used as a dielectricmaterial forming the dielectric layer and the thickness of thedielectric layer is reduced to achieve a reduction in area of theabove-mentioned region and a reduction in the number of the layersmaking up the capacitor.

As conventional electronic components comprising capacitors, a thin-filmcapacitor disclosed in Japanese Published Patent Application(hereinafter referred to as JP-A) 2003-347155 and a thin-film capacitorelement disclosed in JP-A 2003-17366 are known. The thin-film capacitordisclosed in JP-A 2003-347155 incorporates a lower electrode layer, adielectric layer and an upper electrode layer formed one by one on asubstrate through the use of thin-film forming techniques. The thin-filmcapacitor element disclosed in JP-A 2003-17366 incorporates a lowerelectrode, a dielectric layer and an upper electrode formed one by oneon a substrate through the use of thin-film forming techniques. JP-A2003-17366 discloses a technique in which the top surface of the lowerelectrode and that of an insulator layer disposed around the lowerelectrode are flattened to form the dielectric layer on the flattenedtop surfaces. An electronic component formed through thin-film formingtechniques such as the above-mentioned thin-film capacitor and thin-filmcapacitor element is called a thin-film device in the present patentapplication.

JP-A 11-168306 discloses an element comprising: a dielectric substrate;a multilayer thin-film electrode made up of thin-film conductor layersand thin-film dielectric layers alternately stacked on the dielectricsubstrate with a bonding layer disposed between every adjacent thin-filmconductor layer and thin-film dielectric layer; and a flattening filmdisposed between the dielectric substrate and the multilayer thin-filmelectrode. This publication discloses a technique in which polishingprocessing is performed on the top surface of the flattening film sothat the surface roughness Ra of the top surface of the flattening filmis 0.05 μm or smaller.

Since the dielectric layer of the thin-film device comprising acapacitor is formed through thin-film forming techniques, it is possibleto reduce the thickness of the dielectric layer and to thereby reducethe profile of the thin-film device. However, if the thickness of thedielectric layer is reduced in the thin-film device comprising acapacitor, there arise problems that the withstand voltage of thecapacitor is reduced and that variations in withstand voltage of thecapacitor among products are increased. These problems will now bedescribed in detail with reference to FIG. 14.

FIG. 14 is a cross-sectional view illustrating an example ofconfiguration of a thin-film device comprising a capacitor. Thethin-film device of FIG. 14 comprises: a lower conductor layer 102disposed on a substrate 101; a dielectric layer 103 disposed on thesubstrate 101 and the lower conductor layer 102; and an upper conductorlayer 104 disposed in a region sandwiching the dielectric layer 103 withthe lower conductor layer 102. The thin-film device is fabricated byforming the lower conductor layer 102, the dielectric layer 103 and theupper conductor layer 104 in this order on the substrate 101 through theuse of thin-film forming techniques.

In the thin-film device of FIG. 14, a ceramic substrate is used as thesubstrate 101, for example. In this case, even if the top surface of thesubstrate 101 is polished, there exist a number of minute holes in thetop surface of the substrate 101. Accordingly, the surface roughness ofthe top surface of the substrate 101 is great. If the lower conductorlayer 102 is formed on such a substrate 101, the surface roughness ofthe top surface of the lower conductor layer 102 becomes great, too,like the top surface of the substrate 101. If the surface roughness ofthe top surface of the lower conductor layer 102 is great, the thicknessof the dielectric layer 103 is made nonuniform. Consequently, a portionthat is extremely small in thickness develops in the dielectric layer103, and insulation in the portion is degraded, which may result in anextreme reduction in withstand voltage of the capacitor. In such a case,a short-circuit failure of the capacitor resulting from a puncture ofthe dielectric layer 103, for example, is likely to occur. Furthermore,if the thickness of the dielectric layer 103 is nonuniform, variationsin withstand voltage of the capacitor among products are increased.

In a case in which the thin-film device is designed for high frequencyapplications, if the surface roughness of the top surface of the lowerconductor layer 102 is great, the skin resistance of the lower conductorlayer 102 increases, and the signal transmission characteristic of thelower conductor layer 102 may be thereby degraded.

As described above, JP-A 2003-17366 teaches flattening the top surfacesof the lower electrode and the insulator layer disposed around the lowerelectrode and forming the dielectric layer on the flattened topsurfaces. However, this publication does not teach the allowable degreeof surface roughness of the top surface of the lower electrode inrelation to the thickness of the dielectric layer.

As described above, JP-A 11-168306 discloses the technique in which theflattening film is provided between the dielectric substrate and themultilayer thin-film electrode, and polishing processing is performed onthe top surface of the flattening film so that the surface roughness Raof the top surface of the flattening film is 0.05 μm or smaller.However, this publication does not teach the allowable degree of surfaceroughness of the top surface of the flattening film in relation to thethickness of the thin-film dielectric layer.

The foregoing problems apply not only to thin-film devices comprisingcapacitors but also to thin-film devices in general each comprising asubstrate and a lower conductor layer, a dielectric film and an upperconductor layer that are stacked on the substrate.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a thin-film devicecomprising a substrate and a lower conductor layer, a dielectric filmand an upper conductor layer that are stacked on the substrate, thethin-film device being capable of improving the uniformity of thethickness of the dielectric film, and to provide a method ofmanufacturing such a thin-film device.

A thin-film device of the invention comprises: a substrate; a flatteningfilm made of an insulating material and disposed on the substrate; alower conductor layer disposed on the flattening film; a dielectric filmdisposed on the lower conductor layer; and an upper conductor layerdisposed on the dielectric film.

15. In the thin-film device of the invention, the dielectric film has athickness that falls within a range of 0.02 to 1 μm inclusive and thatis smaller than the thickness of the lower conductor layer. The surfaceroughness in maximum height of the top surface of the flattening film issmaller than the surface roughness in maximum height of the top surfaceof the substrate, and is equal to or smaller than the thickness of thedielectric film. The surface roughness in maximum height of the topsurface of the lower conductor layer is equal to or smaller than thethickness of the dielectric film.

A method of manufacturing the thin-film device of the inventioncomprises the steps of: forming the flattening film on the substrate;forming the lower conductor layer on the flattening film; forming thedielectric film on the lower conductor layer; and forming the upperconductor layer on the dielectric film.

According to the thin-film device or the method of manufacturing thesame of the invention, the surface roughness in maximum height of thetop surface of the lower conductor layer is equal to or smaller than thethickness of the dielectric film, so that the thickness of thedielectric film disposed on the lower conductor layer is made uniform.Furthermore, according to the invention, the surface roughness inmaximum height of the top surface of the flattening film disposed on thesubstrate is equal to or smaller than the thickness of the dielectricfilm, so that it is possible to easily reduce the surface roughness inmaximum height of the top surface of the lower conductor layer disposedon the flattening film.

In the thin-film device or the method of the invention, the flatteningfilm may have a thickness that falls within a range of 0.01 to 50 μminclusive.

In the thin-film device or the method of the invention, the lowerconductor layer, the dielectric film and the upper conductor layer mayconstitute a capacitor.

In the method of manufacturing the thin-film device of the invention,the flattening film may be made of an inorganic material, and physicalvapor deposition or chemical vapor deposition may be employed to formthe flattening film in the step of forming the flattening film. In thiscase, the method may further comprise the step of polishing the topsurface of the flattening film, the step being performed after the stepof forming the flattening film and before the step of forming the lowerconductor layer.

In the method of the invention, in the step of forming the flatteningfilm, the flattening film may be formed by applying a material forforming the flattening film to the top of the substrate.

The method of the invention may further comprise the step of polishingthe top surface of the lower conductor layer so that the surfaceroughness in maximum height of the top surface of the lower conductorlayer is equal to or smaller than the thickness of the dielectric film,the step being performed after the step of forming the lower conductorlayer and before the step of forming the dielectric film.

According to the thin-film device or the method of manufacturing thesame of the invention, the surface roughness in maximum height of thetop surface of the lower conductor layer is equal to or smaller than thethickness of the dielectric film, so that the thickness of thedielectric film disposed on the lower conductor layer is made uniform.Furthermore, according to the invention, the surface roughness inmaximum height of the top surface of the flattening film disposed on thesubstrate is equal to or smaller than the thickness of the dielectricfilm, so that it is possible to easily reduce the surface roughness inmaximum height of the top surface of the lower conductor layer disposedon the flattening film. These features of the invention make it possibleto improve the uniformity of the thickness of the dielectric film.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a thin-film device of an embodimentof the invention.

FIG. 2 is a cross-sectional view illustrating a step of a method ofmanufacturing the thin-film device of the embodiment of the invention.

FIG. 3 is a cross-sectional view illustrating a step that follows thestep of FIG. 2.

FIG. 4 is a cross-sectional view illustrating a step that follows thestep of FIG. 3.

FIG. 5 is a cross-sectional view illustrating a step that follows thestep of FIG. 4.

FIG. 6 is a cross-sectional view illustrating a step that follows thestep of FIG. 5.

FIG. 7 is a cross-sectional view illustrating a step that follows thestep of FIG. 6.

FIG. 8 is a cross-sectional view illustrating a step that follows thestep of FIG. 7.

FIG. 9 is a cross-sectional view illustrating a step that follows thestep of FIG. 8.

FIG. 10 is a cross-sectional view illustrating a step that follows thestep of FIG. 9.

FIG. 11 is a cross-sectional view illustrating a step that follows thestep of FIG. 10.

FIG. 12 is a plot showing the relationship between the percent defectiveof the capacitor and the surface roughness in maximum height of the topsurface of the lower conductor layer of the embodiment of the invention.

FIG. 13 is a cross-sectional view illustrating a thin-film device of amodification example of the embodiment of the invention.

FIG. 14 is a cross-sectional view illustrating an example ofconfiguration of a thin-film device comprising a capacitor.

DESCRIPTION OF A PREFERRED EMBODIMENT

A preferred embodiment of the invention will now be described withreference to the accompanying drawings. Reference is now made to FIG. 1to describe a thin-film device of an embodiment of the invention. FIG. 1is a cross-sectional view of the thin-film device of the embodiment. Asshown in FIG. 1, the thin-film device 1 of the embodiment comprises: asubstrate 2; a flattening film 3 made of an insulating material anddisposed on the substrate 2; and a capacitor 4 provided on theflattening film 3. The capacitor 4 incorporates: a lower conductor layer10 disposed on the flattening film 3; a dielectric film 20 disposed onthe lower conductor layer 10; and an upper conductor layer 30 disposedon the dielectric film 20.

Each of the lower conductor layer 10 and the upper conductor layer 30 ispatterned into a specific shape. The dielectric film 20 is disposed tocover the top and side surfaces of the lower conductor layer 10 and thetop surface of the flattening film 3. The upper conductor layer 30 isdisposed in a region sandwiching the dielectric film 20 with the lowerconductor layer 10. The lower conductor layer 10 and the upper conductorlayer 30 make up a pair of electrodes opposed to each other with thedielectric film 20 disposed in between in the capacitor 4.

The substrate 2 is made of an insulating material (a dielectricmaterial). The insulating material forming the substrate 2 may be aninorganic material or an organic material. The insulating materialforming the substrate 2 may be Al₂O₃, for example. The substrate 2 maybe made of a semiconductor material.

A ceramic substrate may be used as the substrate 2. In this case, evenif the top surface of the substrate 2 is polished, there exist a numberof voids or minute holes in the top surface of the substrate 2. Here isgiven a result of examining diameters of voids present in the topsurface of a ceramic substrate when the top surface of the substratemade of Al₂O₃ had been polished, wherein three types of ceramicsubstrates in which the purities of Al₂O₃ were 99.6%, 96% and 93%,respectively, were used. In addition, ten regions each of which was asquare whose side was 0.5 mm long were defined on the top surface ofeach of the ceramic substrates, and a mean void diameter (μm) and amaximum void diameter (μm) in these regions were measured. The resultsof measurement are shown in the table below.

TABLE 1 Purity Mean void diameter Maximum void diameter 99.6% 1.4 4.1  96% 2.7 10   93% 3.1 14

As shown in the table, the higher the purity of Al₂O₃, the smaller arethe mean void diameter and the maximum void diameter. However, thereexist relatively large voids in the top surface of the ceramic substrateeven when the purity is as high as 99.6%. The surface roughness of thetop surface of the ceramic substrate is thereby increased.

In the embodiment the flattening film 3 is formed on the substrate 2, sothat the surface roughness of the base of the lower conductor layer 10is reduced even when a ceramic substrate is used as the substrate 2.

The insulating material forming the flattening film 3 may be aninorganic material or an organic material. An inorganic material formingthe flattening film 3 may be Al₂O₃, for example. When an inorganicmaterial is used as the material of the flattening film 3, it ispreferred to form the flattening film 3 by physical vapor deposition(PVD) or chemical vapor deposition (CVD). An organic material formingthe flattening film 3 may be a resin, for example. In this case, theresin may be either a thermoplastic resin or a thermosetting resin. Whenan organic material such as a resin is used as the material of theflattening film 3, it is preferred that the organic material to form theflattening film 3 be applied to the top of the substrate 2 while thematerial exhibits fluidity, and then the organic material be hardened toform the flattening film 3. The flattening film 3 may be made of aspin-on-glass (SOG) film. The flattening film 3 may be formed through anink-jet technique.

The surface roughness in maximum height Rz of the top surface of theflattening film 3 is smaller than the surface roughness in maximumheight Rz of the top surface of the substrate 2. The surface roughnessin maximum height Rz is one of parameters indicating the surfaceroughness and is defined as a sum of the maximum value of the peak andthe maximum value of the valley of a contour curve of a unit length. Thethickness of the flattening film 3 preferably falls within a range of0.01 to 50 μm inclusive.

If a flattening film made of a conductive material is disposed on thesubstrate 2 in place of the flattening film 3 made of an insulatingmaterial, there arise problems such as one that the lower conductorlayer 10 is brought into conduction, through the flattening film, withanother conductor layer disposed on the flattening film. Therefore, theflattening film 3 made of an insulating material is disposed on thesubstrate 2 in the embodiment.

The lower conductor layer 10 and the upper conductor layer 30 are madeof a conductive material such as Cu. The dielectric film 20 is made of adielectric material. The dielectric material forming the dielectric film20 is preferably an inorganic material. The dielectric material formingthe dielectric film 20 may be any of Al₂O₃, Si₄N₃ and SiO₂, for example.

The thickness of the dielectric film 20 falls within a range of 0.02 to1 μm inclusive, and is smaller than the thickness of the lower conductorlayer 10. The thickness of the dielectric film 20 preferably fallswithin a range of 0.05 to 0.5 μm inclusive. The thickness of the lowerconductor layer 10 preferably falls within a range of 5 to 10 μminclusive. The thickness of the upper conductor layer 30 preferablyfalls within a range of 5 to 10 μm inclusive.

The reason why it is preferred that the thicknesses of the lowerconductor layer 10 and the upper conductor layer 30 fall within theabove-mentioned ranges will now be described. The thin-film device ofthe embodiment is used in a band-pass filter for a wireless local areanetwork (LAN) or for a cellular phone. For the wireless LAN a frequencyband of 2.5 GHz is used. Considering the passing loss in this frequencyband, it is required that the thickness of each of the lower conductorlayer 10 and the upper conductor layer 30 be 3 μm or greater. That is,if the thickness of each of the lower conductor layer 10 and the upperconductor layer 30 is smaller than 3 μm, the passing loss will be toogreat. In addition, a frequency band of 800 MHz to 1.95 GHz is used forcellular phones. To improve the attenuation characteristic of theband-pass filter and to suppress noise at low frequencies in thisfrequency band in particular, it is required that the thickness of eachof the lower conductor layer 10 and the upper conductor layer 30 be 5 μmor greater. Therefore, it is preferred that the thickness of each of thelower conductor layer 10 and the upper conductor layer 30 be 5 μm orgreater. On the other hand, if each of the lower conductor layer 10 andthe upper conductor layer 30 is too thick, the surface roughness of thetop surface of each of the lower conductor layer 10 and the upperconductor layer 30 is increased and the skin resistance of each of thelower conductor layer 10 and the upper conductor layer 30 is therebyincreased, or it becomes necessary to perform flattening processing forreducing the surface roughness of the top surface of each of the lowerconductor layer 10 and the upper conductor layer 30, which requires timeand labor. Therefore, it is practically preferred that the thickness ofeach of the lower conductor layer 10 and the upper conductor layer 30 be10 μm or smaller.

In the embodiment it is defined that the surface roughness in maximumheight Rz of the top surface of the lower conductor layer 10 is equal toor smaller than the thickness of the dielectric film 20. This is definedbased on the result of an experiment that will now be described.

In the experiment, first, a number of samples of the capacitor 4 werefabricated, the samples being different in thickness of the dielectricfilm 20 and in surface roughness in maximum height Rz of the top surfaceof the lower conductor layer 10. The percent defective of the capacitor4 in terms of short-circuit failures was measured for each of thesamples, wherein the percent defective was defined as a percentage ofoccurrences of short-circuit failures of the capacitor 4 when a voltageof 3 volts was applied to each of the samples. The dielectric film 20 ofeach of the samples had a thickness of any of six types, that is, 20 nm,50 nm, 100 nm, 300 nm, 500 nm and 1000 nm. The surface roughness inmaximum height Rz of the top surface of the lower conductor layer 10 ofeach of the samples fell within a range of 1 to 2000 nm inclusive. FIG.12 shows the result of the experiment. FIG. 12 is a plot showing therelationship between the percent defective of the capacitor 4 and thesurface roughness in maximum height Rz of the top surface of the lowerconductor layer 10.

As shown in FIG. 12, in cases where the thickness of the dielectric film20 is any of the above-mentioned six types, a short-circuit failure ofthe capacitor 4 may occur if the surface roughness in maximum height Rzof the top surface of the lower conductor layer 10 is greater than thethickness of the dielectric film 20, whereas no short-circuit failure ofthe capacitor 4 will occur if the surface roughness in maximum height Rzof the top surface of the lower conductor layer 10 is equal to orsmaller than the thickness of the dielectric film 20. This teaches that,as long as the surface roughness in maximum height Rz of the top surfaceof the lower conductor layer 10 is equal to or smaller than thethickness of the dielectric film 20, it is possible to prevent ashort-circuit failure of the capacitor 4 caused by, for example, apuncture of the dielectric film 20 resulting from a reduction inwithstand voltage of the capacitor 4. Because of the foregoing, theembodiment requires that the surface roughness in maximum height Rz ofthe top surface of the lower conductor layer 10 be equal to or smallerthan the thickness of the dielectric film 20.

In addition, the embodiment requires that the surface roughness inmaximum height Rz of the top surface of the flattening film 3 be equalto or smaller than the thickness of the dielectric film 20. If the lowerconductor layer 10 is formed on the flattening film 3, the surfaceroughness in maximum height Rz of the top surface of the lower conductorlayer 10 is close to that of the top surface of the flattening film 3.Therefore, as long as the surface roughness in maximum height Rz of thetop surface of the flattening film 3 is equal to or smaller than thethickness of the dielectric film 20, it is possible to easily make thesurface roughness in maximum height Rz of the top surface of the lowerconductor layer 10 equal to or smaller than the thickness of thedielectric film 20 without performing any flattening processing on thetop surface of the lower conductor layer 10 or by performing simpleflattening processing on the top surface of the lower conductor layer10. Because of the foregoing, the embodiment requires that the surfaceroughness in maximum height Rz of the top surface of the flattening film3 be equal to or smaller than the thickness of the dielectric film 20.

Reference is now made to FIG. 2 to FIG. 11 to describe a method ofmanufacturing the thin-film device 1 of the embodiment. Althoughexamples of materials and thicknesses of the layers are given in thefollowing description, those examples are non-limiting for the method ofthe embodiment.

FIG. 2 is a cross-sectional view illustrating a step of the method ofmanufacturing the thin-film device 1 of the embodiment. In the method,first, as shown in FIG. 2, the flattening film 3 is formed on thesubstrate 2. Here is given an example in which the substrate 2 is aceramic substrate wherein the purity of Al₂O₃ is 99.6% and the topsurface of the substrate is polished. In this case, the maximum voiddiameter in the top surface of the substrate 2 is 4.1 μm, for example.Here, by way of example, the insulating material forming the flatteningfilm 3 is Al₂O₃ that is an inorganic material, and the flattening film 3is formed by PVD or CVD. The flattening film 3 thus formed is moreclosely packed than a ceramic. The thickness of the flattening film 3 atthis point is 5.5 μm, for example.

Next, as shown in FIG. 3, the top surface of the flattening film 3 isflattened by polishing so that the surface roughness in maximum heightRz of the top surface of the flattening film 3 is equal to or smallerthan the thickness of the dielectric film 20 that will be formed later.For example, when the dielectric film 20 having a thickness of 0.1 μm isto be made, the top surface of the flattening film 3 is polished so thatthe surface roughness in maximum height Rz of the top surface of theflattening film 3 is equal to or smaller than 0.1 μm. A method of thispolishing is chemical mechanical polishing (CMP), for example. Thethickness of the flattening film 3 polished is 2.0 μm, for example.Here, by way of example, the surface roughness in maximum height Rz ofthe top surface of the flattening film 3 polished is 30 nm. The methodof polishing the top surface of the flattening film 3 is not limited toCMP but may be any other polishing method such as buffing, lapping anddie polishing. The processing of flattening the top surface of theflattening film 3 may be performed by a combination of two or morepolishing methods.

The flattening film 3 made of Al₂O₃ and formed by PVD or CVD is veryclosely packed as described above. As a result, there exist no minuteholes in the top surface of the flattening film 3 polished, such asholes existing in the top surface of a ceramic substrate polished. It istherefore possible by polishing the top surface of the flattening film 3to easily flatten the top surface of the flattening film 3 so that thesurface roughness in maximum height Rz of the top surface of theflattening film 3 is equal to or smaller than the thickness of thedielectric film 20.

It is not necessary to flatten the top surface of the flattening film 3by polishing in such a case that the surface roughness in maximum heightRz of the top surface of the flattening film 3 is equal to or smallerthan the thickness of the dielectric film 20 without flattening the topsurface of the flattening film 3.

The flattening film 3 may be made of an organic material such as aresin. In this case, the flattening film 3 may be formed in such amanner that the organic material to form the flattening film 3 isapplied to the top of the substrate 2 while the material exhibitsfluidity, and then the organic material is hardened. The flattening film3 may be made of a spin-on-glass (SOG) film. The flattening film 3 maybe formed through an ink-jet technique. In these cases, it is possibleto make the surface roughness in maximum height Rz of the top surface ofthe flattening film 3 equal to or smaller than the thickness of thedielectric film 20 without polishing the top surface of the flatteningfilm 3.

Next, as shown in FIG. 4, a first electrode film 11 and a secondelectrode film 12 are formed one by one on the substrate 2 bysputtering, for example. The electrode films 11 and 12 will be used aselectrodes when a plating film is formed by electroplating later andwill make up part of the lower conductor layer 10. The material of thefirst electrode film 11 is Ti, for example. The thickness of the firstelectrode film 11 is 5 nm, for example. The material of the secondelectrode film 12 is Cu or Ni, for example. The thickness of the secondelectrode film 12 is 100 nm, for example. Alternatively, a single-layerelectrode film may be formed in place of the electrode films 11 and 12.

FIG. 5 illustrates the following step. In the step, first, a photoresistlayer having a thickness of 8 μm, for example, is formed on theelectrode film 12. Next, the photoresist layer is patterned byphotolithography to form a frame 40. The frame 40 has a groove 41 havinga shape corresponding to the shape of the lower conductor layer 10 to beformed.

Next, as shown in FIG. 6, the plating film 13 is formed in the groove 41by electroplating using the electrode films 11 and 12 as electrodes. Thematerial of the plating film 13 is Cu, for example. The thickness of theplating film 13 is 9 to 10 μm, for example.

Next, as shown in FIG. 7, the top surface of the plating film 13 isflattened by polishing so that the surface roughness in maximum heightRz of the top surface of the plating film 13 is equal to or smaller thanthe thickness of the dielectric film 20 that will be formed later. Forexample, when the dielectric film 20 having a thickness of 0.1 μm is tobe made, the top surface of the plating film 13 is polished so that thesurface roughness in maximum height Rz of the top surface of the platingfilm 13 is equal to or smaller than 0.1 μm. A method of this polishingis CMP, for example. The polishing is performed such that the thicknessof the plating film 13 polished is 8 μm, for example. The method ofpolishing the top surface of the plating film 13 is not limited to CMPbut may be any other polishing method such as buffing, lapping and diepolishing. The processing of flattening the top surface of the platingfilm 13 may be performed by a combination of two or more polishingmethods. Next, as shown in FIG. 8, the frame 40 is removed.

In the step shown in FIG. 6, if the plating film 13 is formed so thatthe thickness of the plating film 13 is greater than the thickness ofthe frame 40, portions of the plating film 13 out of the groove 41 ofthe frame 40 may be polished, and polishing may be stopped when thethickness of the plating film 13 coincides with that of the frame 40 inthe step shown in FIG. 7. In this case, it is possible to preciselycontrol the thickness of the lower conductor layer 10 formed of theplating film 13. Furthermore, if the amount of polishing of the frame 40is great, the polishing device such as a grindstone may be loaded, andflattening of the top surface of the plating film 13 may be therebydisturbed. Such a failure can be prevented if the polishing is stoppedwhen the thickness of the plating film 13 coincides with that of theframe 40.

In the embodiment the top surface of the flattening film 3 issufficiently flat so that the surface roughness in maximum height Rz ofthe top surface of the flattening film 3 is equal to or smaller than thethickness of the dielectric film 20. Consequently, it is likely that thetop surface of the plating film 13 formed above the flattening film 3with the electrode films 11 and 12 disposed in between is flat.Therefore, it is not necessary to flatten the top surface of the platingfilm 13 by polishing in such a case that the surface roughness inmaximum height Rz of the top surface of the plating film 13 is equal toor smaller than the thickness of the dielectric film 20 withoutpolishing the top surface of the plating film 13. Furthermore, in theembodiment, also in the case in which the top surface of the platingfilm 13 is flattened by polishing, it is easy to flatten the top surfaceof the plating film 13 so that the surface roughness in maximum heightRz of the top surface of the plating film 13 is equal to or smaller thanthe thickness of the dielectric film 20.

Next, as shown in FIG. 9, the electrode films 11 and 12 except portionsthereof located below the plating film 13 are removed by dry etching orwet etching. As a result, the lower conductor layer 10 is formed of theremaining electrode films 11 and 12 and the plating film 13. If thematerial of each of the electrode film 12 and the plating film 13 is Cu,a portion of the plating film 13 is etched, too, when etching isperformed to remove the electrode films 11 and 12. However, there ishardly any difference between the surface roughness of the top surfaceof the plating film 13 before this etching and that after this etching.If the material of the electrode film 12 is Ni and the material of theplating film 13 is Cu, a condition under which the plating film 13 isnot etched is chosen for the etching for removing the electrode films 11and 12. The surface roughness in maximum height Rz of the top surface ofthe lower conductor layer 10 formed in the step shown in FIG. 9 is equalto or smaller than the thickness of the dielectric film 20 that will beformed later.

In the steps shown in FIG. 5 to FIG. 9, the plating film 13 patternedthrough the use of the frame 40 is formed and then the electrode films11 and 12 except the portions thereof located below the plating film 13are removed to form the lower electrode layer 10. Instead of employingsuch a process, the lower electrode layer 10 may be formed by forming anunpatterned plating film on the entire top surfaces of the electrodefilms 11 and 12 and then removing portions of the plating film and theelectrode films 11 and 12. Alternatively, the lower electrode layer 10may be formed by forming an unpatterned conductor film on the flatteningfilm 3 by PVD such as sputtering or evaporation and then etching aportion of the conductor film. When the lower electrode layer 10 isformed by PVD, in particular, it is possible to make the surfaceroughness in maximum height Rz of the top surface of the lower electrodelayer 10 equal to or smaller than the thickness of the dielectric film20 without polishing the top surface of the lower electrode layer 10.

When the lower conductor layer 10 is formed by electroplating, it ispreferred to adjust the sizes of precipitation grains by controlling thecomposition of plating bath and the current density. In addition, whenthe lower conductor layer 10 is formed by electroplating, it ispreferred that, for suppressing a change in the surface roughness of thetop surface of the lower conductor layer 10 with time, heat treatment beperformed on the lower conductor layer 10 so that the lower conductorlayer 10 is in equilibrium and then the dielectric film 20 be formed onthe lower conductor layer 10. When the lower conductor layer 10 isformed by PVD, heat treatment of the lower conductor layer 10 is notrequired since it is nearly in the state of equilibrium.

Next, as shown in FIG. 10, the dielectric film 20 is formed bysputtering, for example, to cover the top and side surfaces of the lowerconductor layer 10 and the top surface of the flattening film 3. Thethickness of the dielectric film 20 is 0.1 μm, for example.

Next, as shown in FIG. 11, the upper conductor layer 30 is formed in aregion that is on the dielectric film 20 and that sandwiches thedielectric film 20 with the lower conductor layer 10. A method offorming the upper conductor layer 30 is the same as that of the lowerconductor layer 10 except the flattening processing. That is, electrodefilms 31 and 32 are first formed in this order on the dielectric film20. The materials and thicknesses of the electrode films 31 and 32 arethe same as those of the electrode films 11 and 12. Next, a photoresistlayer having a thickness of 8 μm, for example, is formed on theelectrode film 32. Next, the photoresist layer is patterned byphotolithography to form a frame not shown. The frame has a groovehaving a shape corresponding to the shape of the upper conductor layer30 to be formed. Next, a plating film 33 is formed in the groove byelectroplating using the electrode films 31 and 32 as electrodes. Thematerial of the plating film 33 is Cu, for example. The thickness of theplating film 33 is 8 μm, for example. Next, the frame is removed. Next,the electrode films 31 and 32 except portions thereof located below theplating film 33 are removed by dry etching or wet etching. As a result,the upper conductor layer 30 is formed of the remaining electrode films31 and 32 and the plating film 33.

According to the embodiment as thus described, the flattening film 3 isformed on the substrate 2, and the surface roughness in maximum heightRz of the top surface of the flattening film 3 is made equal to orsmaller than the thickness of the dielectric film 20. The lowerconductor layer 10 and the dielectric film 20 are then formed one by oneon the flattening film 3. Therefore, according to the embodiment, it iseasy to flatten the top surface of the lower conductor layer 10 so thatthe surface roughness in maximum height Rz thereof is equal to orsmaller than the thickness of the dielectric film 20. As a result, it ispossible to improve the uniformity of the thickness of the dielectricfilm 20. It is thereby possible to suppress a reduction in withstandvoltage of the capacitor 4 and an increase in variation in withstandvoltage of the capacitor 4 among products. For example, it is possibleto make the withstand voltage of the capacitor 4 equal to or greaterthan 80 volts if the top surface of the lower conductor layer 10 isflattened as in the embodiment under a condition in which the withstandvoltage of the capacitor 4 is equal to or smaller than 30 volts if thetop surface of the lower conductor layer 10 is not flattened.Furthermore, according to the embodiment, since a reduction in withstandvoltage of the capacitor 4 is suppressed, it is possible to prevent ashort-circuit failure of the capacitor 4 caused by a puncture of thedielectric film 20, for example.

According to the embodiment, since the thickness of the dielectric film20 is made uniform, it is possible to make the dielectric film 20 thinwhile maintaining a sufficient withstand voltage of the capacitor 4. Asa result, in cases where capacitors having the same capacitances are tobe implemented, it is possible to reduce the area of a region in whichthe lower conductor layer 10 and the upper conductor layer 30 areopposed to each other with the dielectric film 20 disposed in betweenand to reduce the number of conductor layers and dielectric films to bestacked. It is thereby possible to achieve reductions in dimensions andprofile of the thin-film device.

Furthermore, according to the embodiment, since the surface roughness ofthe top surface of the lower conductor layer 10 is small, it is possibleto reduce the skin resistance of the lower conductor layer 10. As aresult, it is possible to prevent degradation of the signal transmissioncharacteristic of the lower conductor layer 10 when the thin-film device1 is designed for high frequency applications.

In the embodiment, inverse sputtering may be performed before formingthe dielectric film 20 to remove unwanted substances such as oxides andorganic substances present on the surface of the lower conductor layer10 and to activate the surface of the lower conductor layer 10 so as toimprove the contact of the surface of the lower conductor layer 10 withthe dielectric film 20. In this case, in particular, processing ofimproving the contact of the surface of the lower conductor layer 10with the dielectric film 20 and processing of forming the dielectricfilm 20 may be performed consecutively in a single vacuum chamber, sothat the contact of the lower conductor layer 10 with the dielectricfilm 20 is further improved.

It is also possible that, before forming the electrode film 11 or 31,inverse sputtering is performed to remove unwanted substances such asoxides and organic substances present on the surface of the base of theelectrode film 11 or 31 and to improve the contact of the surface of thebase with the electrode film 11 or 31.

In the step of forming the lower conductor layer 10 or the step offorming the upper conductor layer 30, inverse sputtering is employed,for example, as the method of removing the electrode films except theportions thereof located below the plating film. In this case, there isa possibility of damaging the top surface of the lower conductor layer10, the upper conductor layer 30 or the dielectric film 20, depending onthe conditions for the inverse sputtering. Methods for preventing thisinclude removing the electrode films by wet etching, and adjusting theoutput and duration of inverse sputtering when the electrode films areremoved by inverse sputtering. Alternatively, a film of a material (suchas Ni) that is not used for the electrode films may be formed byplating, for example, on the plating film made of Cu, for example, andthe electrode films may be selectively etched by inverse sputtering.Another alternative is that, a sputter film of Cu may be formed on theplating film made of Cu, for example. In this case, the crystal graindiameter of the sputter film is smaller than that of the plating film,and therefore it is possible to prevent the top surface of the lowerconductor layer 10 or the upper conductor layer 30 from being damaged byinverse sputtering.

In the case of performing inverse sputtering after the dielectric film20 is formed and before the electrode film 31 is formed, and/or in thecase of removing the electrode films 31 and 32 by inverse sputtering toform the upper conductor layer 30, it is necessary to adjust theconditions for the inverse sputtering such as the output, gas flow rate,and process time so as to prevent a reduction in thickness of thedielectric film 20 and damage to the dielectric film 20.

Reference is now made to FIG. 13 to describe a modification example ofthe embodiment. FIG. 13 is a cross-sectional view of the thin-filmdevice of the modification example. In the thin-film device 1 of themodification example, a portion of the top surface of the substrate 2 isexposed at the top surface of the flattening film 3. Such a structurecan be formed when the top surface of the flattening film 3 is flattenedby polishing after the flattening film 3 is formed on the substrate 2.In the modification example, it suffices that the surface roughness inmaximum height Rz of the surface made up of the top surface of theflattening film 3 and the portion of the top surface of the substrate 2exposed at the top surface of the flattening film 3 is equal to orsmaller than the thickness of the dielectric film 20. The remainder ofconfiguration, function and effects of the modification example aresimilar to those of the thin-film device 1 of FIG. 1.

The present invention is not limited to the foregoing embodiment but maybe practiced in still other ways. For example, in the thin-film deviceof the invention, a protection film may be provided on the upperconductor layer 30, or the upper conductor layer 30 may be exposed.Furthermore, one or more additional layers may be provided above theupper conductor layer 30.

In the invention, another dielectric film and conductor layer may bealternately stacked in a total of two or more layers on the top surfaceof the upper conductor layer 30. As a result, it is possible to form acapacitor having a configuration in which conductor layers anddielectric films are alternately stacked in a total of five or morelayers.

The lower conductor layer, the dielectric film and the upper conductorlayer of the invention are not limited to the ones constituting acapacitor. For example, each of the lower conductor layer and the upperconductor layer may make up an individual signal line, and thedielectric film may be used to insulate the lower and upper conductorlayers from each other.

The thin-film device of the invention may include elements other than acapacitor. Such elements may be passive elements such as inductors andresistors, or may be active elements such as transistors. Such elementsmay be lumped-constant elements or distributed-constant elements.

The thin-film device of the invention may comprise terminals disposed onsides, the bottom surface or the top surface. The thin-film device ofthe invention may comprise through holes for connecting a plurality ofconductor layers. The thin-film device of the invention may compriseconductor layers for wiring for connecting the lower conductor layer 10or the upper conductor layer 30 to terminals or other elements.Alternatively, portions of the lower conductor layer 10 or the upperconductor layer 30 may also serve as the terminals, or the lowerconductor layer 10 or the upper conductor layer 30 may be connected tothe terminals via through holes.

If the thin-film device of the invention incorporates a capacitor andelements other than the capacitor, the thin-film device may be used as avariety of circuit components including a capacitor, such as LC circuitcomponents, various filters including low-pass filters, high-passfilters and band-pass filters, diplexers, and duplexers.

The thin-film device of the invention is utilized for a mobilecommunications apparatus such as a cellular phone and a communicationsapparatus for a wireless LAN.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

1. A thin-film device comprising: a substrate; a flattening film made ofan insulating material and disposed on the substrate; a lower conductorlayer disposed on the flattening film; a dielectric film disposed on thelower conductor layer; and an upper conductor layer disposed on thedielectric film, wherein: the dielectric film has a thickness that fallswithin a range of 0.02 to 1 μm inclusive and that is smaller than athickness of the lower conductor layer; a portion of a top surface ofthe substrate is exposed at a top surface of the flattening film; asurface roughness in maximum height of the top surface of the flatteningfilm is smaller than a surface roughness in maximum height of the topsurface of the substrate, and is equal to or smaller than the thicknessof the dielectric film; and a surface roughness in maximum height of atop surface of the lower conductor layer is equal to or smaller than thethickness of the dielectric film.
 2. The thin-film device according toclaim 1, wherein the flattening film has a thickness that falls within arange of 0.01 to 50 μm inclusive.
 3. The thin-film device according toclaim 1, wherein the lower conductor layer, the dielectric film and theupper conductor layer constitute a capacitor.
 4. A method ofmanufacturing a thin-film device comprising a substrate, a flatteningfilm made of an insulating material and disposed on the substrate, alower conductor layer disposed on the flattening film, a dielectric filmdisposed on the lower conductor layer, and an upper conductor layerdisposed on the dielectric film, wherein: the dielectric film has athickness that falls within a range of 0.02 to 1 μm inclusive and thatis smaller than a thickness of the lower conductor layer; a portion of atop surface of the substrate is exposed at a top surface of theflattening film; a surface roughness in maximum height of the topsurface of the flattening film is smaller than a surface roughness inmaximum height of the top surface of the substrate and is equal to orsmaller than the thickness of the dielectric film; and a surfaceroughness in maximum height of a top surface of the lower conductorlayer is equal to or smaller than the thickness of the dielectric film,the method comprising the steps of: forming the flattening film on thesubstrate; polishing the top surface of the flattening film so that theportion of the top surface of the substrate is exposed at the topsurface of the flattening film, forming the lower conductor layer on theflattening film; forming the dielectric film on the lower conductorlayer; and forming the upper conductor layer on the dielectric film. 5.The method according to claim 4, wherein the flattening film has athickness that falls within a range of 0.01 to 50 μm inclusive.
 6. Themethod according to claim 4, wherein the lower conductor layer, thedielectric film and the upper conductor layer constitute a capacitor. 7.The method according to claim 4, wherein: the flattening film is made ofan inorganic material; and physical vapor deposition or chemical vapordeposition is employed to form the flattening film in the step offorming the flattening film.
 8. The method according to claim 4,wherein, in the step of forming the flattening film, the flattening filmis formed by applying a material for forming the flattening film to atop of the substrate.
 9. The method according to claim 4, furthercomprising the step of polishing the top surface of the lower conductorlayer so that the surface roughness in maximum height of the top surfaceof the lower conductor layer is equal to or smaller than the thicknessof the dielectric film, the step being performed after the step offorming the lower conductor layer and before the step of forming thedielectric film.